The present invention relates to an anti-backlash nut assembly, and more particularly to an anti-backlash nut assembly for use in a type of jack known commonly as a worm gear screw jack, and in linear actuators.
Worm gear screw jacks of the type employing a non-rotating jack screw extended and retracted by a worm gear threaded thereon, with the worm gear driven by a worm shaft oriented perpendicular to the jack screw, are well known. Two examples of such are shown in U.S. Pat. No. 3,176,963, issued to Sturm Apr. 6, 1965, and U.S. Pat. No. 3,323,777, issued to McMullen Jun. 6, 1967, both of which are incorporated herein by reference to the extent necessary to complete this disclosure.
In many worm gear screw jacks, the jack screw is made of hardened steel while the worm gear is made of a softer material such as aluminum bronze. As a result, the interior threads of the worm gear tend to wear due to friction, ultimately introducing backlash or end play into the jack when the load switches between tension and compression.
In the past, attempts have been made to eliminate this backlash. One such method used is to split the worm gear in half and provide for each half to be axially spaced from the other. The worm gear halves are then clampingly engaged on the jack screw threads and timed together with pins. However, such a solution suffers from the disadvantage of breaking up the worm gear tooth contact with the worm shaft, thereby increasing the pressure on the worm gear threads. In addition, the pins are subject to bending, resulting in misalignment of the worm gear halves, subjecting the worm gear to additional friction loading.
Another attempt to eliminate backlash uses a separate anti-backlash nut rotatably driven by the worm gear. The nut is adjusted to apply pressure to the jack screw thread faces opposite those faces in contact with the interior threads of the worm gear. The McMullen patent discussed above discloses such an arrangement.
However, the driving pins of McMullen are still subject to significant bending forces since a segment thereof extending transverse to the longitudinal axis of the pin is not supported by a collar or like housing mechanism.
Linear actuators of the type employing an axially traveling nut assembly driven back and forth by a rotating screw threaded therethrough are well known. Two examples of such are shown in U.S. Pat. No. 4,954,032, issued to Morales Sep. 4, 1990, and U.S. Pat. No. 4,008,625, issued to Malhotra Feb. 22, 1997, both of which are incorporated herein by reference.
Such traveling nut assemblies typically include two nut disposed in end-to-end relation to each other. The nuts are free to move axially relative to each other while being rotationally fixed relative to each other by means of axially extending splines or fingers. However, such splines and fingers tend to be subject to bending or breaking at unsupported portions thereof as a result of bending moments or shear forces acting transverse to their long axes.